Layered, light-emitting element

ABSTRACT

A light-emitting element is provided having a layered structure composed of at least a light-emitting layer having a light-emitting region and a reflective layer for reflecting light emitted from the light-emitting region. Light emitted from the light-emitting region is extracted from a light-extracting surface distanced from the light-emitting region. A light-scattering portion is present in a part of the reflective layer.

TECHNICAL FIELD

The present invention relates to a self-luminous light-emitting element,a substrate provided with the light-emitting elements, and a displaydevice and a lighting device that utilize the light-emitting element(s).

BACKGROUND ART

Light-emitting elements that emit light by applying an electric fieldthereto, such as electroluminescent (EL) elements and light-emittingdiodes, are self-luminous, and thus have high visibility and can be madethin. For these reasons, such elements are attracting attention aslighting devices such as backlights and as display devices such as flatpanel displays. Above all, organic EL elements that use organiccompounds as emitters can be driven at low voltages, can be easily madelarge in area, and can easily obtain the desired emission color byselecting appropriate dyes, and thus are being actively developed asnext-generation displays.

For an EL element using an organic emitter, blue light emission isobtained by, for example, applying a voltage of 30 V to avapor-deposited anthracene film with a thickness of 1 μm or less (ThinSolid Films, 94 (1982) 171). However, this element did not achievesufficient luminance even when a high voltage was applied to theelement, and thus required further improvement in luminescenceefficiency.

On the other hand, Tang et. al. made an element in which a transparentelectrode (anode), a hole transport material layer, an electrontransport luminescent material layer, and a cathode using a low workfunction metal were stacked on top of each other, so as to improveluminescence efficiency. The element achieved a luminance of 1000 cd/m²with an applied voltage of 10 V or less (Appl. Phys. Lett., 51 (1987)913).

Furthermore, there have been reported an element having a three-layerstructure in which a luminescent material layer was sandwiched between ahole transport material layer and an electron transport material layer(Jpn. J. Appl. Phys., 27 (1988) L269), and an element that obtainedlight emission from a dye doped in a light-emitting layer (J. Appl.Phys., 65 (1989) 3610).

A cross-sectional view of the general configuration of a prior-artorganic EL element is shown in FIG. 26. In the drawing, referencenumeral 71 denotes a transparent substrate made, for example, of glass,plastic, or the like, reference numeral 72 denotes a transparent anodemade, for example, of indium tin oxide (ITO), reference numeral 73denotes a hole transport material layer made, for example, ofN,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),reference numeral 74 denotes an electron transport luminescent materiallayer made, for example, of tris(8-quinolinolato)aluminum (Alq₃), andreference numeral 75 denotes a cathode made, for example, of an AlLialloy. Reference numeral 76 denotes a light-emitting layer. When avoltage is applied to the element in the direction shown in the drawing,holes are injected from the anode 72 into the hole transport materiallayer 73, and electrons are injected from the cathode 75 into theelectron transport luminescent material layer 74. The holes injectedfrom the anode 72 pass through the hole transport material layer 73, andthen are injected into the electron transport luminescent material layer74. The holes and electrons are recombined in the electron transportluminescent material layer 74, thereby exciting molecules of Alq₃, fromwhich light emission is obtained.

The transparent anode made of ITO is typically formed by sputtering,electron-beam evaporation, or the like. The hole transport materiallayer and the electron transport luminescent material layer, made oforganic substances such as TPD and Alq₃, and the cathode made of an AlLialloy or the like, are typically formed by resistive heatingevaporation.

An example of light-emitting elements other than the above-mentionedorganic EL element is an inorganic EL element. A cross-sectional view ofthe general configuration of an inorganic EL element is shown in FIG.27. In the drawing, reference numeral 81 denotes a transparent substratemade, for example, of glass, reference numeral 82 denotes a transparentelectrode made, for example, of ITO, reference numeral 83 denotes afirst insulating material layer made, for example, of Ta₂O₅, referencenumeral 84 denotes a luminescent material layer made, for example, ofMn-doped ZnS, reference numeral 85 denotes a second insulating materiallayer made, for example, of Ta₂O₅, and reference numeral 86 denotes arear electrode made, for example, of Al. Reference numeral 87 denotes alight-emitting layer. When an alternating electric field is applied toboth electrodes of the element, electrons moved from the interfacesbetween the insulating material layers and the luminescent materiallayer are accelerated, and thereby collide with and excite Mn, which isthe luminescent center. Upon returning to the ground state, lightemission occurs.

One of the factors contributing to the limited luminescence efficiencyof these light-emitting elements is the external extraction efficiencyof light emitted from the light-emitting layer (external extractionefficiency). For example, as shown in FIG. 28, of light emitted from anelectron transport luminescent material layer 94 by application of avoltage to an anode 92 and a cathode 95, such light as to have anglesequal to or greater than the critical angle is totally reflected at aninterface between a hole transport material layer 93 and the transparentelectrode 92, at an interface between the transparent electrode 92 and atransparent substrate 91, or at an interface between the transparentsubstrate 91 and air (i.e., a light-extracting surface), and thereforecannot be extracted outside the element. The external extractionefficiency is expressed by: 1/(2n²), where n is the refractive index ofthe luminescent material layer (Adv. Mater. 6 (1994) p.491). In atypical organic EL element, the refractive index of the luminescentmaterial layer is about 1.6 and the external extraction efficiency isabout 20%. In an inorganic EL element, when ZnS with a refractive indexof about 2.3 is used as the luminescent material layer, the externalextraction efficiency is about 10%. Hence, even when the internalquantum efficiency (which is the conversion efficiency of injectedelectric charges into light) is 100%, because of the limitation byexternal extraction efficiency, the external quantum efficiency turnsout to be on the order of 10% to 20%.

Various methods have been investigated to improve external extractionefficiency. For example, there have been suggested: (1) a method offorming light reflective films at the edges of the substrate (seeJapanese Unexamined Patent Publication No. 61-195588 and the like); (2)a method that uses a substrate having light condensing characteristicsof lens or the like (see Japanese Examined Patent Publication No.2670572, Japanese Unexamined Patent Publication No. 4-192290, Patent No.2773720, Japanese Unexamined Patent Publication No. 10-172756, JapaneseUnexamined Patent Publication No. 10-223367, and the like); and (3) amethod in which a light-emitting layer or substrate is formed in a mesaform (see Japanese Unexamined Patent Publication No. 4-306589, Opt.Lett. vol. 27, No. 6 (1997) p.396, and the like).

The above-mentioned method (1) is such that light reflective films areprovided at the edges of the substrate, whereby light, which ispropagated mainly through the substrate and then diffracted from theedges of the substrate, is condensed onto a light-extracting surface.However, in the case, for example, of a so-called dot matrix display inwhich very small light-emitting elements are arranged in a matrix, it isvery difficult to form such reflective films on every light-emittingelement which corresponds to a unit pixel.

In the case of the above-mentioned method (2) in which the lightextraction side of a substrate has a lens configuration, even whenlight-emitting elements and lenses are disposed at a one-to-one ratio ina dot matrix display such as one described above, because light emittedfrom a very small single light-emitting element is isotropicallyemitted, most of the light, which has passed through the substrate witha certain thickness and reached the light extraction side, is incidenton the lens on the adjacent pixel side. Accordingly, the effect on theimprovement of the efficiency of the light-emitting element, which isthe object, is little, and besides, the problem of image blur occurs. Inorder to overcome the problem, there has been suggested a method ofpositioning light-emitting regions and lenses as close as possible toeach other by, for example, implanting lenses in the substrate (JapaneseUnexamined Patent Publication No. 10-172756). This method inhibits suchimage blur as to be described above and the like, but has difficulty inmanufacturing.

The above-mentioned method (3) has difficulty in processing a substrate.

DISCLOSURE OF THE INVENTION

In view of the foregoing and other problems, it is an object of thepresent invention to provide a light-emitting element that can befabricated easily and has high external light extraction efficiency. Itis another object of the present invention to provide a substrateprovided with light-emitting elements in which image blur due to leakedlight is minimized. It is still another object of the present inventionto provide a display device and a lighting device that use such alight-emitting element(s) and such a substrate provided withlight-emitting elements.

The present inventors have conducted a concentrated investigation toattain the above objects, and consequently have found that it ispossible to extract light, which would conventionally be confined withina light-emitting layer, a transparent electrode, or a transparentsubstrate and could not be extracted outside the element, by:positioning, by focusing attention on the thickness of the layers withinwhich light is confined, a light-emitting region of a light-emittinglayer and a light-extracting surface close to each other such that totalreflection does not occur and providing a layer with a refractive indexof approximately 1 (first aspect); providing a light-scattering portionto change the incident angle of light on the light-extracting surface(second aspect); providing a light-scattering portion and examininggeometrical optics ray paths (third aspect); combining the constructionof the first aspect and a part of the construction of the second aspect(fourth aspect); or combining the construction of the first aspect andthe construction of the third aspect (fifth aspect). Thereby, theexternal extraction efficiency is improved, attaining high luminescenceefficiency. In addition, provision of a high-grade display device and ahigh-grade lighting device was made possible.

Light-emitting Element

(First Aspect)

According to a first aspect of the present invention, there is provideda light-emitting element having a layered structure, the layeredstructure comprising at least a light-emitting layer having alight-emitting region, the light-emitting element comprising, a layerwith a refractive index of approximately 1, wherein a distance between asurface of the light-emitting region facing a side of the layer with arefractive index of approximately 1 and a surface of the layer with arefractive index of approximately 1 facing a side of the light-emittingregion, is limited to 50% or less of a peak wavelength of light.

With the above construction, because the distance between the surface ofthe light-emitting region facing the side of the layer with a refractiveindex of approximately 1 and the surface of the layer with a refractiveindex of approximately 1 facing the side of the light-emitting region isvery small, Snell's law or the like is not applicable. Accordingly, itbecomes possible to extract light that was confined within thelight-emitting element due to total reflection and could not beextracted outside the element. This improves external extractionefficiency, making it possible to provide a light-emitting element withhigh luminescence efficiency. In such a light-emitting element, byfocusing attention on the thickness of individual layers, the individuallayers can be made thin so that the light-emitting region and thelight-extracting surface are close to each other, and thus fabricationis easy. In addition, in this light-emitting element, because theindividual layers are very thin, the element contributes to a reductionin thickness of a display device or lighting device.

As used herein, the term “light-emitting region” refers to a regionwhere light emission actually occurs by application of a voltage. Whenthe distance between the surface of the light-emitting region facing theside of the layer with a refractive index of approximately 1 and thesurface of the layer with a refractive index of approximately 1 facingthe side of the light-emitting region, is equal to or smaller than aparticular distance (optical distance), light emitted therefrom does notapply to Snell's law or the like, and consequently, it becomes possibleto extract light that conventionally could not be extracted. The reasonfor providing a layer with a refractive index of approximately 1 is asfollows. When a passivation layer, which will be described later, isformed directly on a transparent electrode layer (a second electrodelayer, as will be described later), the distance between thelight-emitting region and the outside the element becomes large,increasing the amount of light to be totally reflected. On the otherhand, when a layer with a refractive index of approximately 1, which hassubstantially the same refractive index as air (refractive index: 1), isinterposed between the passivation layer and the transparent electrodelayer, the above-described drawback can be overcome.

In addition, on a substrate, a light reflective first electrode layer,the light-emitting layer, a transparent second electrode layer, and thelayer with a refractive index of approximately 1 may be provided in thisorder.

Even with a light-emitting element having, on the substrate, thereflective electrode, light-emitting layer, and transparent electrodestacked on top of each other in this order, as with the aboveconstruction, the external extraction efficiency is increased, as is thecase above. In addition, since light is extracted from the opposite sidefrom the substrate, light cannot be propagated through the thicksubstrate.

Further, a passivation layer may be formed on the layer with arefractive index of approximately 1.

When a passivation layer is thus formed on the layer with a refractiveindex of approximately 1, while a reduction in external extractionefficiency is prevented, the light-emitting element is sufficientlyprotected, resulting in an increase in mechanical strength.

On a substrate, a reflective layer, a first transparent electrode layer,the light-emitting layer, a second transparent electrode layer, and thelayer with a refractive index of approximately 1 may be provided in thisorder.

Furthermore, a passivation layer may be formed on the layer with arefractive index of approximately 1.

The distance between a surface of the light-emitting region facing aside of the layer with a refractive index of approximately 1 and asurface of the layer with a refractive index of approximately 1 facing aside of the light-emitting region, may be limited to 30% or less, andpreferably 20% or less, and particularly preferably 10% or less of thepeak wavelength of light.

With such a construction, the external extraction efficiency is furtherincreased.

A distance t between a reflective layer and an interface may be limitedto 500 μm or less.

With such a construction, as is the case described above, the externalextraction efficiency is increased. In addition, since light isextracted from the opposite side from the substrate, light cannot bepropagated through the thick substrate.

In the case of extracting light from the substrate side, when theconstruction is such that a layer with a refractive index ofapproximately 1, an underlying layer made of SiO₂, a transparent firstelectrode layer, a light-emitting layer having a light-emitting region,and a second electrode layer serving as a reflective electrode areprovided on a substrate, the distance between a surface of thelight-emitting region facing the side of the layer with a refractiveindex of approximately 1 and a surface of the layer with a refractiveindex of approximately 1 facing the side of the light-emitting regionbecomes larger due to the presence of the underlying layer made of SiO₂,and thus such a structure is not desirable.

An example of the layer with a refractive index of approximately 1includes an aerogel layer. The same applies to the following aspects.

(Second Aspect)

The present aspect attempts to improve external extraction efficiency byproviding a light-scattering portion to change the incident angle oflight on the light-extracting surface, and to inhibit, in terms ofgeometrical optics, image blur and the like caused by leaked light. Amore detailed description is given below.

According to a second aspect of the present invention, there is provideda light-emitting element having a layered structure, the layeredstructure comprising: a light-emitting layer; a light-extracting surfacefor extracting light emitted from the light-emitting layer; a reflectivelayer for reflecting light emitted from the light-emitting layer, thereflective layer being provided opposite the light-emitting layer; aninterface at which a refractive index decreases in a direction ofextracting light from the light-emitting layer; and a light-scatteringportion provided at least on a surface of the reflective layer, on aportion in contact with the interface, or between the reflective layerand the light-emitting layer, the light-emitting element wherein, thefollowing Equation (1) is satisfied:t<(n cos θ/2)×L  (1),where t is a distance between the reflective layer and the interface, Lis a longest distance between any two points in an in-plane direction ofthe light-emitting element, θ is a critical angle for the interface, andn is a refractive index of the light-emitting layer.

Light emitted from the light-emitting region is isotropically emitted,and then either, depending on the incident angle of the light on thelight-extracting surface, extracted outside the element or reflected offthe light-extracting surface and confined within the element. That is,light with an incident angle less than the critical angle is extractedoutside the element, while light at the critical angle or greater istotally reflected and confined within the element. A light-emittingelement having the above construction, however, has a light-scatteringportion within the element, and thus the confined light can be scatteredwithin the element, making it possible to change the incident angle ofthe light on the light-extracting surface. Accordingly, since lighthaving an incident angle less than the critical angle can be extractedoutside the element, the external extraction efficiency is increased ascompared to prior-art elements.

In addition, with a substrate provided with light-emitting elements thatsatisfy the above Equation (1), most of the light emitted from alight-emitting region of a single light-emitting element is extractedoutside the element from a light-extracting surface of the singlelight-emitting element, and thus it is possible to inhibit the lightfrom being extracted from a light-extracting surface of anotherlight-emitting element adjacent to the single light-emitting element. Asa result, it is possible to provide a display device and a lightingdevice, in which image blur and the like caused by leaked light areinhibited.

In the above light-emitting element, the light-scattering portion maycorrespond to an irregular surface of the reflective layer. Thelight-scattering portion may correspond to an irregular surface of alight reflective first electrode layer. The light-scattering portion maycorrespond to an irregular surface of an insulating and reflectivelayer. In addition, in the above light-emitting element, thelight-scattering portion may correspond to an irregular surface of thelight-extracting surface. When the light-scattering portion has anirregular surface, as is described above, light can be scattered easily.The maximum value (R_(max)) of surface roughness of the irregularsurface is desirably ¼ or more of the peak wavelength of light. On theirregular surface, a planarizing layer for planarizing the irregularsurface may be provided. The planarizing layer may be made of a polymer.In addition, the planarizing layer may be made of a conductive polymer.

Furthermore, the light-scattering portion may be made of a base materialand an additive to be dispersed in the base material, and the basematerial and the additive may have different refractive indices. Thedispersion may be performed uniformly or non-uniformly. A transparentsecond electrode layer may also serve as the light-scattering portion,the transparent second electrode layer including an additive dispersedin ITO, the ITO being a base material, the additive being one selectedfrom the group consisting of inorganic particles and metal particles.Moreover, a light-scattering layer may be additionally formed, which mayinclude an additive dispersed in a polymer, the polymer being a basematerial, the additive being one selected from the group consisting ofinorganic particles and metal particles.

The light-scattering portion may be provided on a surface of thereflective layer, on a portion in contact with the interface, or betweenthe reflective layer and the light-emitting layer.

A layer with a refractive index of approximately 1 may be formed on afilm at the interface. In this case, an exposed surface of the layerwith a refractive index of approximately 1 may serve as thelight-extracting surface. Further, a passivation layer may be formed onthe layer with a refractive index of approximately 1. In this case, anexposed surface of the passivation layer may serve as thelight-extracting surface.

There may be no additional layer on a film at the interface, and theinterface may serve as the light-extracting surface.

(Third Aspect)

The present aspect attempts to further improve mainly the externalextraction efficiency by providing a light-scattering portion in a partof the reflective layer. A more detailed description is given below.

There is provided a light-emitting element having a layered structure,the layered structure comprising at least a light-emitting layer havinga light-emitting region and a reflective layer for reflecting lightemitted from the light-emitting region, the light-emitting elementextracting light from a light-extracting surface distanced from thelight-emitting region, the light being emitted from the light-emittingregion, wherein a light-scattering portion is present in a part of thereflective layer.

Light emitted from the light-emitting region is isotropically emitted,and then either, depending on the incident angle of the light on thelight-extracting surface, extracted outside the element or reflected offthe light-extracting surface and confined within the element. That is,light with an incident angle less than the critical angle is extractedoutside the element, while light at the critical angle or greater istotally reflected and confined within the element. A light-emittingelement having the above construction, however, has a light-scatteringportion within the element, and thus the confined light can be scatteredwithin the element, making it possible to change the incident angle ofthe light on the light-extracting surface. Accordingly, since lighthaving an incident angle less than the critical angle can be extractedoutside the element, the external extraction efficiency is increased ascompared to prior-art elements.

The layered structure may comprise at least the light-emitting layer anda first electrode layer for reflecting light emitted from thelight-emitting region, and the reflective layer may be composed of thefirst electrode layer.

A non-light emitting surface may be present in a part of the firstelectrode layer, and the light-scattering portion may be provided on thenon-light emitting surface.

When the reflective layer is made in a form of an island or lattice, therelative area of the electrode layer is reduced accordingly, making itpossible to reduce power consumption.

The form of an island is particularly desirable.

This is because when the reflective layer is in the form of an island,it becomes possible to effectively extract light emitted from thelight-emitting region that corresponds to such a form. Specifically, ina light-emitting element having a reflective layer formed in allin-plane directions, it is possible, for example, that light may beextracted from a light-extracting surface of an adjacent light-emittingelement. On the other hand, when the reflective layer is in the form ofan island, more light can be extracted from a targeted light-extractingsurface, and therefore the external extraction efficiency of thetargeted light-extracting surface is improved. In addition, since thelight-scattering portion is present on the same plane as the reflectivelayer in the form of an island, the element can be made thin.

When the reflective layer is in the form of an island, there may be aplurality of the reflective layers in the form of an island.

When there is an interface, at which a refractive index decreases in adirection from the light-emitting layer to the light-extracting surface,between the light-emitting layer and the light-extracting surface, thefollowing Equation (1) may be satisfied:t<(n cos θ/2)×L  (1),where t is a distance between the reflective layer and the interface, Lis a longest distance between any two points in an in-plane direction ofthe light-emitting element, θ is a critical angle for the interface, andn is a refractive index of the light-emitting layer.

With such a construction, image blur and the like caused by leaked lightcan be inhibited, as is the case described above.

In the above light-emitting element, the light-scattering portion maycorrespond to an irregular surface of the reflective layer. In addition,the light-scattering portion may correspond to an irregular surface ofthe light reflective first electrode layer. The light-scattering portionmay correspond to an irregular surface of an insulating and reflectivelayer. Moreover, in the above light-emitting element, thelight-scattering portion may correspond to an irregular surface of thelight-extracting surface. When the light-scattering portion has anirregular surface, as is described above, light can be scattered easily.The maximum value (R_(max)) of surface roughness of the irregularsurface is desirably ¼ or more of the peak wavelength of light. On theirregular surface, a planarizing layer for planarizing the irregularsurface may be provided. The planarizing layer may be made of a polymer.In addition, the planarizing layer may be made of a conductive polymer.

(Fourth Aspect)

The present aspect attempts to further improve mainly the externalextraction efficiency by combining the construction of the first aspectand a part of the construction of the second aspect. A more detaileddescription is given below.

There is provided a light-emitting element having a layered structure,the layered structure comprising at least a light-emitting layer havinga light-emitting region, the light-emitting element extracting lightfrom a light-extracting surface distanced from the light-emittingregion, the light being emitted from the light-emitting region, thelight-emitting element comprising: a layer with a refractive index ofapproximately 1; and a light-scattering portion, wherein a distancebetween a surface of the light-emitting region facing a side of thelayer with a refractive index of approximately 1 and a surface of thelayer with a refractive index of approximately 1 facing a side of thelight-emitting region, is limited to 50% or less of a peak wavelength oflight.

With this construction, most of the light emitted from thelight-emitting region is extracted outside the element without beingreflected. Even if the light is reflected, the incident angle of thelight on the light-extracting surface becomes less than the criticalangle due to the presence of the light-scattering portion, and thus thelight is extracted outside the element, further increasing externalextraction efficiency.

It is to be noted, however, that a layer with a refraction index ofapproximately 1 is not essential. Even without the layer with arefraction index of approximately 1, similar function and effect tothose described above can be obtained. In such a case, the distancebetween the surface of the light-emitting region facing a side of thelight-extracting surface and the light-extracting surface may be limitedto 50% or less of the peak wavelength of light.

In the present aspect, modifications may be made in such a manner as tobe made to the constructions of the first and second aspects.

(Fifth Aspect)

The present aspect attempts to further improve mainly the externalextraction efficiency by combining the construction of the first aspectand the construction of the third aspect. A more detailed description isgiven below.

There is provided a light-emitting element having a layered structure,the layered structure comprising at least a light-emitting layer havinga light-emitting region, the light-emitting element extracting lightfrom a light-extracting surface distanced from the light-emittingregion, the light being emitted from the light-emitting region, thelight-emitting element comprising, a layer with a refractive index ofapproximately 1, wherein: a distance between a surface of thelight-emitting region facing a side of the layer with a refractive indexof approximately 1 and a surface of the layer with a refractive index ofapproximately 1 facing a side of the light-emitting region, is limitedto 50% or less of a peak wavelength of light; and the layered structureincludes a reflective layer for reflecting light emitted from thelight-emitting region, a light-scattering portion being present in apart of the reflective layer.

With this construction, most of the light emitted from thelight-emitting region is extracted outside the element without beingreflected. Even if the light is reflected, the incident angle of thelight on the light-extracting surface becomes less than the criticalangle due to the presence of the light-scattering portion, and thus thelight is extracted outside the element, further increasing externalextraction efficiency.

It is to be noted, however, that a layer with a refraction index ofapproximately 1 is not essential. Even without the layer with arefraction index of approximately 1, similar function and effect tothose described above can be obtained. In such a case, the distancebetween the surface of the light-emitting region facing a side of thelight-extracting surface and the light-extracting surface may be limitedto 50% or less of the peak wavelength of light.

In the present aspect, modifications may be made in such a manner as tobe made to the construction of the first aspect and a part of theconstruction of the third aspect.

Display Device

A display device of the present invention may utilize any one of thelight-emitting elements described in the first to fifth aspects.

Lighting Device

A lighting device of the present invention may utilize any one of thelight-emitting elements described in the first to fifth aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 2 of the present invention.

FIG. 3 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 3 of the present invention.

FIG. 4 is a diagram illustrating the theoretical construction of thelight-emitting element according to Embodiment 3 of the presentinvention.

FIG. 5 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 4 of the present invention.

FIG. 6 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 5 of the present invention.

FIG. 7 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 6 of the present invention.

FIG. 8 is a cross-sectional view schematically showing a modifiedexample of the light-emitting element according to Embodiment 6 of thepresent invention.

FIGS. 9( a) and 9(b) are schematic views of a light-emitting elementaccording to Embodiment 7 of the present invention. FIG. 9( a) is across-sectional view of the light-emitting element and FIG. 9( b) is aplan view showing a surface where a reflective electrode and alight-scattering layer are present.

FIGS. 10( a) and 10(b) are schematic views of a light-emitting elementaccording to Embodiment 8 of the present invention. FIG. 10( a) is across-sectional view of the light-emitting element and FIG. 10( b) is aplan view showing a surface where reflective electrodes and alight-scattering layer are present.

FIG. 11 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 9 of the present invention.

FIG. 12 is a cross-sectional view schematically showing a modifiedexample of the light-emitting element according to Embodiment 9 of thepresent invention.

FIG. 13 is a cross-sectional view schematically showing a light-emittingelement according to Example 1.

FIG. 14 is a cross-sectional view schematically showing a light-emittingelement according to Example 5.

FIG. 15 is a cross-sectional view schematically showing a light-emittingelement according to Example 6.

FIG. 16 is a cross-sectional view schematically showing a light-emittingelement according to Example 7.

FIG. 17 is a cross-sectional view schematically showing a light-emittingelement according to Example 8.

FIG. 18 is a cross-sectional view schematically showing a light-emittingelement according to Example 9.

FIG. 19 is a cross-sectional view schematically showing a light-emittingelement according to Example 11.

FIG. 20 is a cross-sectional view schematically showing a light-emittingelement according to Example 24.

FIG. 21 is a schematic cross-sectional view of the main part of thelight-emitting element according to Example 24 for illustrating thefabrication method thereof.

FIG. 22 is a schematic cross-sectional view of the main part of thelight-emitting element according to Example 24 for illustrating thefabrication method thereof.

FIG. 23 is a schematic cross-sectional view of the main part of thelight-emitting element according to Example 24 for illustrating thefabrication method thereof.

FIG. 24 is a schematic cross-sectional view of the main part of thelight-emitting element according to Example 24 for illustrating thefabrication method thereof.

FIG. 25 is a graph showing the relationship between extractionefficiency T and d/λ.

FIG. 26 is a cross-sectional view schematically showing a prior-artorganic EL element.

FIG. 27 is a cross-sectional view schematically showing a prior-artinorganic EL element.

FIG. 28 is a schematic view showing extraction of light in a prior-artlight-emitting element.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are described below withreference to the drawings.

Embodiment 1

FIG. 1 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 1, which corresponds to the foregoingfirst aspect. The light-emitting element is constructed such that on asubstrate 1 a reflective electrode 2 (a light-reflective first electrodelayer), a light-emitting layer 4 having a light-emitting region 3(specifically, the light-emitting layer comprises an electron-injectinglayer, an electron transport luminescent material layer, a holetransport material layer, a buffer layer, and the like), a transparentelectrode 5 (a transparent second electrode layer), an aerogel layer 7with a refractive index of approximately 1, and a passivation layer 8are stacked on top of each other in this order. A surface of thepassivation layer 8 serves as a light-extracting surface 6.

For the substrate 1, any type of substrate can be used as long as it cansupport the light-emitting element. It is possible to use a resinsubstrate made, for example, of polycarbonate, polymethyl methacrylate,or polyethylene terephthalate, a silicon substrate, or the like, inaddition to a glass substrate.

The reflective electrode 2 should have high reflectivity and anelectrode function that allows the light-emitting layer 4 to efficientlyemit light. It is therefore desirable to use a metal film made of Al oran Al compound, silver or a silver compound, or the like. For the silvercompound, an alloy of silver, palladium, and copper (AgPdCu) or an alloyof silver, gold, and copper (AgAuCu) is desirably used. In the case of aso-called current injection type organic EL element using an organiccompound for the luminescent material layer, the reflective electrodenormally serves as a cathode or anode. For the cathode, a material withgood electron-injection efficiency, i.e., a material with a low workfunction, is often used. For the anode, a material with good holeinjection efficiency, i.e., a material with a high work function or highionization potential, is often used. For the cathode of an organic ELelement, for example, an alloy of a metal with a low work function andhigh reactivity (Li, Mg, or the like) and a metal with low reactivityand good stability (Al, Ag, or the like), such as an AlLi alloy or anMgAg alloy, can be used. Alternatively, it is also possible to use alayered electrode made of a metal with a low work function or a compoundthereof and a metal with a high work function, such as Li/Al or LiF/Al.In forming the reflective electrode, sputtering, electron-beamevaporation, resistive heating evaporation, and the like can beemployed.

In the case of an organic EL element, the light-emitting region 3 of thelight-emitting layer 4 is made of an organic compound such as Alq₃. Thelight-emitting layer 4 may have a single layer structure or a multilayerstructure in which layers are divided by function. In the case of themultilayer structure, as is the case with prior-art structures, it ispossible to employ, for example, a two-layer structure consisting of ahole transport material layer using TPD or the like and an electrontransport luminescent material layer using Alq₃ or the like, athree-layer structure consisting of a hole transport material layerusing TPD or the like, a luminescent material layer using perylene orthe like, and an electron transport material layer using oxadiazole orthe like, or a multilayer structure consisting of more than threelayers. It is to be noted that the hole transport material layer isdisposed on the hole-injecting electrode side such as ITO, and theelectron transport material layer is disposed on the electron-injectingelectrode side such as AlLi or MgAg. In the case of an organic ELelement, the light-emitting layer is formed mostly by resistive heatingevaporation; however, it is also possible to employ electron-beamevaporation, sputtering, and the like.

In the case of an inorganic EL element, as is the case with prior-artstructures, for example, a structure is employed in which a luminescentmaterial layer, which is made of ZnS or the like doped with Mn or thelike, is sandwiched between insulating material layers made of Ta₂O₅ orthe like. These layers are mostly formed by sputtering, but it is alsopossible to employ electron-beam evaporation, resistive heatingevaporation, ion plating, and the like.

For the transparent electrode 5, normally, one with a lighttransmittance of more than 50% is used. For example, it is possible touse a transparent electrode of oxide such as indium tin oxide (ITO) ortin oxide or a metal thin film electrode with a thickness of the orderof 5 nm to several tens of nm. The transparent electrode can be formedby sputtering, resistive heating evaporation, electron-beam evaporation,ion plating, and the like.

In the case of an organic EL element, when the substrate having formedthereon a light-emitting layer, is heated to high temperatures, thelight-emitting layer is degraded, and therefore a transparent electrodeneeds to be deposited at low temperatures. Further, in cases where anITO film or the like, serving as a transparent electrode, is formed bysputtering, electron-beam evaporation, or the like, it is desirable toform a buffer layer between the light-emitting layer and the transparentelectrode so as to reduce damage to the light-emitting layer. For thebuffer layer, a thermally stable organic compound such as copperphthalocyanine is suitably used. It is to be noted that when, forexample, a transparent metal thin film, such as MgAg, with a filmthickness of the order of 10 nm is used, damage to the light-emittinglayer can be reduced, and thus it is not necessary to provide a bufferlayer.

The aerogel layer 7 was prepared as follows. A solution, in which methylsilicate, methanol, water, and ammonia were mixed, was spin coated ontothe transparent electrode 5 in air saturated with methanol vapor, andthen was placed in air saturated with methanol vapor for a given time,thereby forming a wetting gel. Next, the microskeleton of silicacontained in this wetting gel thin film was hydrophobized withhexamethyldisilazane, and then the solution included in the wetting gelthin film was extracted and removed with carbonic acid gas with 80° C.and 16 Mp, thereby preparing a hydrophobic silica aerogel thin film(aerogel layer).

The passivation layer 8 was prepared by forming SiO₂ on the aerogellayer 7 by EB evaporation or sputtering.

Here, when the distance d between the surface of the light-emittingregion 3 facing the side of the aerogel layer 7 and the surface of theaerogel layer 7 facing the side of the light-emitting region 3, islimited to 50% or less of the peak wavelength of light, most of theemitted light is extracted outside the element without being reflected.Accordingly, the light-emitting element turns out to have higherexternal extraction efficiency and higher luminescence efficiency thanprior-art light-emitting elements. In particular, the distance d betweenthe surface of the light-emitting region 3 facing the side of theaerogel layer 7 and the surface of the aerogel layer 7 facing the sideof the light-emitting region 3 is preferably 30% or less, and morepreferably 20% or less, and most preferably 10% or less of the peakwavelength of light.

Now, the principle of improvement of external extraction efficiency ofthe present embodiment is described. A prior-art element comprises, fromthe transparent substrate side, an anode electrode (transparentelectrode)/light-emitting layer/cathode electrode (reflectiveelectrode). Light emitted from a light-emitting region of thelight-emitting layer is transmitted through the transparent electrodeand the transparent substrate, and then extracted from the transparentsubstrate side. The light emitted from the light-emitting region isrefracted, when transmitted through the transparent electrode and thelike, at interfaces according to Snell's law. Then, at an interfacebetween a light-extracting surface, i.e., the transparent substrate, andair, light at the critical angle or greater is totally reflected andconfined within the transparent substrate, light-emitting layer, ortransparent electrode. In the case, for example, of an organic ELelement, when the refractive index of the light-emitting layer is 1.6,of light produced in the light-emitting layer, only such light as tohave a solid angle of up to 39° can be extracted outside the element. Onthe other hand, an element of the present embodiment comprises, from thesubstrate side, a cathode electrode (reflective electrode)/organiclight-emitting layer/anode electrode (transparent electrode). Lightemitted from a light-emitting region of the light-emitting layer isextracted after having been transmitted through the transparentelectrode or after having been reflected off the reflective electrode.In this case, when the distance d between the surface of thelight-emitting region facing the aerogel layer side and the surface ofthe aerogel layer facing the light-emitting region side is 50% or lessof the peak wavelength of light, Snell's law or the like is notapplicable because the optical path length is very short. Consequently,most of the light at the critical angle or greater can be extractedoutside the element without being reflected off the light-extractingsurface.

Embodiment 2

FIG. 2 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 2, which corresponds to the foregoingfirst aspect. In the light-emitting element, a light-emitting region 3exists in contact with a transparent electrode 5. In an element havingsuch a construction, when the film thickness of the transparentelectrode 5 is 50% or less of the peak wavelength of light emitted fromthe light-emitting region, most of the light at the critical angle orgreater is not reflected due to the same principle as above, and thusthe external extraction efficiency is increased.

Embodiments 1 and 2 described the case where a reflective electrode wasused; however, even when an insulating and reflective layer, which ismade, for example, of a mixture of a highly light reflective substancesuch as TiO₂ or BaTiO₃ and a highly dielectric substance such ascyanoethyl cellulose, is provided between the substrate and the firstelectrode or between the first electrode and the light-emitting layer,the external extraction efficiency is increased due to the sameprinciple.

Embodiment 3

FIG. 3 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 3, which corresponds to the foregoingsecond aspect. The light-emitting element is constructed such that on asubstrate 1 a reflective electrode 12 having a light-scattering surface(irregular surface) 11, serving as a light-scattering portion, alight-emitting layer 4 having a light-emitting region 3, and atransparent electrode 5 are stacked on top of each other in this order.The surface of the transparent electrode 5 serves as a light-extractingsurface 6.

In the present embodiment, a substrate provided with light-emittingelements, comprising a substrate and a plurality of the above-describedlight-emitting elements disposed on the substrate, was constructed suchthat the relationship between the distance between a reflective layer(the reflective electrode or an insulating and reflective layer)composing the light-emitting element, and the light-extracting surface,and the longest distance between any two points in the in-planedirection (of the surface where the reflective layer is present) of thelight-emitting element is specified by the critical angle or the like,so as to avoid mixing lights between adjacent light-emitting elements. Amore detailed description is given below.

In the substrate provided with light-emitting elements of the presentembodiment, the distance t between the reflective layer and thelight-extracting surface, and the longest distance L between any twopoints in the in-plane direction of the light-emitting element, aredetermined to satisfy the following Equation (1):t<(n cos θ/2)×L  (1)where θ is the critical angle for the light-extracting surface and n isthe refractive index of the light-emitting region.

The introduction of the above equation is described below with referenceto FIG. 4. It is to be noted that the drawing is simplified to describethe introduction of the equation.

In the drawing, of light emitted from a light-emitting region of alight-emitting element 32, such light as to have been reflected off areflective layer 30 is directed toward a light-extracting surface 6. Atthis point, while light at less than the critical angle θ with respectto the light-extracting surface 6 is extracted outside the element,light at the critical angle θ or greater is totally reflected. In such acase, when t and L satisfy the relationship “t<L/(2 tan θ)”, the totallyreflected light reaches the reflective layer of the same element andthus is not directed toward a reflective layer of any adjacentlight-emitting element. Here, since θ is the critical angle, theequation “n×sin θ=1” is obtained. In addition, since tan θ=sin θ/cos θ,by combining these equations, the above Equation (1) is introduced. InFIG. 4, reference numeral 31 denotes a portion through which lightemitted from the light-emitting region is transmitted. Specifically, theportion corresponds to a transparent electrode, a light-emitting layer,and the like.

When Equation (1) is satisfied, most of the light emitted within asingle light-emitting element is supposed to be extracted from alight-extracting surface of the single light-emitting element. Thus, incases where adjacent light-emitting elements emit light with differentcolors, the colors are not mixed, and therefore problems such as imageblur can be suppressed.

In addition, according to the present embodiment, the externalextraction efficiency is improved for the following reason. A prior-artelement comprises, from the transparent substrate side, an anodeelectrode (transparent electrode)/light-emitting layer/cathode electrode(reflective electrode with a flat surface). In this element, lightemitted from a light-emitting region of the light-emitting layer isextracted from the transparent substrate side after having beentransmitted through the transparent electrode and the transparentsubstrate. At this point, light at the critical angle or greater istotally reflected at an interface (light-extracting surface) between thetransparent substrate and air, or the like, and is confined within thetransparent substrate, transparent electrode, or light-emitting layer.On the other hand, in an element of the present embodiment, since alight-scattering surface is present, during multiple reflection betweena light-extracting surface and a reflective electrode surface, thereflected light is scattered by the light-scattering surface, wherebythe reflected light partly enters at an angle less than the criticalangle and then is extracted straight outside the element. Consequently,the external extraction efficiency is improved.

It is desirable that the light-scattering surface 11 be capable ofisotropically scattering light that is emitted from the light-emittingregion. For the surface roughness of the light-scattering surface 11, inorder to obtain satisfactory scattering effects, the maximum value(R_(max)) is desirably ¼ or more of the peak wavelength of light emittedfrom the light-emitting region.

The light-scattering surface 11 can be formed by heating the substrateduring the formation of a reflective electrode, or by forming areflective electrode and then heat treating the reflective electrode toinduce crystal growth of the metal film, thereby forming irregularitieson the surface of the film. For another method, it is also possible thatafter forming a reflective electrode, a surface of the reflectiveelectrode may be mechanically roughened by sandblasting or the like. Forstill another method, after roughening a substrate surface by mechanicalprocesses such as sandblasting, by physical etching processes using, forexample, ion beam, or by chemical etching processes using, for example,acid or alkali, a reflective electrode may be formed so as to conform tothe shape of the irregular substrate surface.

When an element has such a construction as to be described in thepresent embodiment, in which a reflective electrode/light-emittinglayer/transparent electrode are provided from the transparent substrateside, light is extracted from the transparent electrode side, preventinglight from traveling in the lateral direction during multiplereflections within the thick substrate. Accordingly, in cases where aplurality of elements, each is of the order of several hundred μm squarein size, are disposed, as in a dot-matrix display, it is possible toinhibit light from being emitted from a location away from an emittedelement in the lateral direction.

Embodiment 4

FIG. 5 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 4, which corresponds to the foregoingsecond aspect. This light-emitting element differs from a light-emittingelement of Embodiment 3 in that a transparent electrode 13 is used inplace of the reflective electrode 12, and beneath the transparentelectrode (on the substrate side) there are provided a light-scatteringlayer 14, which has a light-scattering surface (irregular surface)serving as a light-scattering portion, and a planarizing layer 15 forplanarizing the light-scattering surface.

The light-scattering layer 14 does not function as an electrode, andtherefore any material, even with low electrical conductivity, can besuitably used for the light-scattering layer as long as the material hashigh light reflectivity and is capable of isotropically scattering lightemitted from a light-emitting region. This provides the advantage of awide selection of materials. Specifically, in addition to a metal filmof Al or an Al compound, silver or a silver compound, or the like, it isalso possible to use a mixture of a highly light reflective substancesuch as TiO₂ or BaTiO₃ and a highly dielectric substance such ascyanoethyl cellulose, or the like. The light-scattering layer can beformed by a method in which after depositing a light-scattering layerusing the above-described materials, the surface of the layer isroughened, for example, by mechanical processes such as sandblasting, byphysical etching processes using, for example, ion beam, or by chemicaletching processes using, for example, acid or alkali.

The planarizing layer 15 should be a transparent insulating film; forexample, inorganic materials such as SiO₂ or polymer materials such aspolymethyl methacrylate (PMMA) can be used. In the case of the inorganicmaterials such as SiO₂, a film can be deposited by sputtering,electron-beam evaporation, or the like. A polymer film of, for example,PMMA or the like can be deposited by coating methods such as spincoating and casting. When the planarizing layer 15 is provided, as isthe case with the present embodiment, the possibility of a short circuitcan be reduced as compared with an element of Embodiment 3.

As the transparent electrode 13, a transparent electrode of oxide suchas ITO or tin oxide, a metal thin film with a thickness of the order of5 nm to several tens of nm, or the like can be used, as is the case withthe transparent electrode 5.

Embodiment 4 described the case where an insulating material was usedfor the planarizing layer; however, it is also possible to make theconstruction one in which the planarizing layer is formed using aconductive material such as a conductive polymer so as to use such aplanarizing layer as an electrode. This construction improves externalextraction efficiency by the same principle as above, and contributes toa reduction in the thickness and size of the element.

Embodiment 5

FIG. 6 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 5, which corresponds to the foregoingsecond aspect. This light-emitting element differs from a light-emittingelement of Embodiment 3 in that the surface of a reflective electrode 12is not made to serve as a light-scattering surface and alight-scattering surface 16 is made to serve as a light-extractingsurface. By employing such a construction, the amount of light incidentat angles less than the critical angle is increased, resulting in anincrease in external extraction efficiency.

The light-scattering surface 16 can be formed, for example, by forming atransparent electrode 5 and then providing a surface rougheningtreatment to a surface of the transparent electrode by mechanicalprocesses such as sandblasting, by physical etching processes using, forexample, ion beam, or the like. It is also possible to employ a methodin which a transparent material layer is formed on a transparentelectrode and then etched.

Embodiment 6

FIG. 7 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 6, which corresponds to the foregoingsecond aspect. This light-emitting element differs from a light-emittingelement of Embodiment 3 in that the surface of a reflective electrode 2is not made to serve as a light-scattering surface and alight-scattering layer 9 is additionally formed on the light-extractingsurface side. By employing such a construction, the amount of lightincident at angles less than the critical angle is increased, resultingin an increase in external extraction efficiency.

The light-scattering layer 9 is prepared by dispersing SiO₂ (refractiveindex: about 1.5) or the like in a polymer such as polymethylmethacrylate (PMMA, refractive index: about 1.7) or polycarbonate (PC,refractive index: about 1.7).

It is to be noted that the light-scattering layer 9 is not necessarilyto be additionally formed to obtain the above function and effect; forexample, it is also possible to make a structure one in which, as shownin FIG. 8, SiO₂ (refractive index: about 1.5) or the like is dispersedin a transparent electrode 5. Such a structure eliminates the necessityof additionally forming the light-scattering layer 9, and thusmanufacturing costs can be reduced.

Embodiment 7

FIGS. 9( a) and 9(b) are schematic views showing a light-emittingelement according to Embodiment 7, which corresponds to the foregoingthird aspect. FIG. 9( a) is a cross-sectional view of the element, andFIG. 9( b) is a plan view showing the surface where a reflectiveelectrode 2 and a light-scattering layer 14 are present. Thislight-emitting element differs from a light-emitting element ofEmbodiment 3 in that the reflective electrode (with a flat surface) 2and the light-scattering layer (a light-scattering portion) 14 areprovided in different sections on the same plane. Specifically, theconstruction of Embodiment 3 is such that the reflective electrode isdisposed on the entire surface of one side of the light-emitting layerand the entire surface of the reflective electrode is made to serve as alight-scattering surface. On the other hand, the construction of thepresent embodiment is such that the reflective electrode 2 is disposedon a part of one side of the light-emitting layer 4 and thelight-scattering layer 14 is disposed on the other part of the one sideof the light-emitting layer 4.

With the above construction, since a light-emitting region 3 is presentabove the reflective electrode 2 and light emitted from thelight-emitting region 3 can be extracted from the entire surface of alight-extracting surface 6 by, for example, total reflection of theemitted light at the light-extracting surface and scattering of theemitted light by the light-scattering portion, it is possible to extractlight more efficiently than the element of Embodiment 3. Specifically,the portion to which a voltage is applied (or the portion through whichan electric current flows) during operation is a region corresponding tothe area of the reflective electrode in the in-plane direction in thelight-emitting layer (i.e., the light-emitting region 3). Light emittedfrom this region is totally reflected off the light-extracting surface,is reflected off the reflective electrode, or is scattered by thelight-scattering portion. Hence, the light-extracting surface above thelight-emitting region has a larger area than the area of thelight-emitting region in the in-plane direction. Therefore, the entireouter surface of the light-emitting element on the transparent electrodeside functions as a light-extracting surface, and light is extractedtherefrom, making it possible to extract light more efficiently.

Embodiment 8

FIGS. 10( a) and 10(b) are cross-sectional views schematically showing alight-emitting element according to Embodiment 8, which corresponds tothe foregoing third aspect. This light-emitting element differs from alight-emitting element of Embodiment 7 in that a plurality of (four)reflective electrodes 2 in the form of an island are present. With sucha construction, since light-emitting portions of the light-emittingregions and the light-scattering portions are close to each other, it ispossible to scatter light more efficiently. As a result, light can bemore efficiently extracted outside the element.

Embodiment 9

FIG. 11 is a cross-sectional view schematically showing a light-emittingelement according to Embodiment 9, which corresponds to the foregoingthird aspect. This light-emitting element differs from a light-emittingelement of Embodiment 8 in that a reflective electrode 2 in the form ofan island also serves as a light-scattering layer 14.

It is to be noted, however, that the shape is not limited to the onedescribed above; it is also possible to form a light-scattering layer 14on a flat reflective electrode 2, as shown in FIG. 12.

Embodiments 3 to 9 described the case where a reflective electrode wasused; however, even when an insulating and reflective layer, which ismade, for example, of a mixture of a highly light reflective substancesuch as TiO₂ or BaTiO₃ and a highly dielectric substance such ascyanoethyl cellulose, is provided between the substrate and the firstelectrode or between the first electrode and the light-emitting layer,the external extraction efficiency is increased by the same principle.In the case where such an insulating and reflective layer is provided,the insulating and reflective layer may be made to serve as alight-scattering portion (light-scattering surface).

Embodiment 10

The present embodiment corresponds to the foregoing fourth aspect. Alight-emitting element of the present embodiment comprises an aerogellayer with a refractive index of approximately 1, and the distancebetween the surface of a light-emitting region facing the aerogel layerside and the surface of the aerogel layer facing the light-emittingregion side, is limited to 50% or less, and preferably 30% or less, andmore preferably 20% or less, and most preferably 10% or less of the peakwavelength of light. In addition, the light-emitting element has alight-scattering portion. When the construction is made to satisfy theboth conditions as described above, most of the light emitted from thelight-emitting region can be extracted outside the element withoutundergoing total reflection. Even if the light is totally reflected,because the incident angle of the light on the light-extracting surfacebecomes less than the critical angle due to the presence of thelight-scattering portion, the light is extracted outside the element,resulting in a further improvement in external extraction efficiency ascompared with prior-art light-emitting elements.

It is to be noted, however, that the aerogel layer is not essential;similar advantageous effects can be obtained even without the aerogellayer.

Embodiment 11

The present embodiment corresponds to the foregoing fifth aspect. Alight-emitting element of the present embodiment comprises an aerogellayer with a refractive index of approximately 1, and the distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side, is limited to 50% or less, and preferably30% or less, and more preferably 20% or less, and most preferably 10% orless of the peak wavelength of light. In addition, the layered structureincludes a reflective layer for reflecting light emitted from thelight-emitting region, and a light-scattering portion is present in apart of the reflective layer. When the construction is made to satisfythe both conditions as described above, most of the light emitted fromthe light-emitting region can be extracted outside the element withoutundergoing total reflection. Even if the light is totally reflected,because the incident angle of the light on the light-extracting surfacebecomes less than the critical angle due to the presence of thelight-scattering portion, the light is extracted outside the element,resulting in a further improvement in external extraction efficiency ascompared with prior-art light-emitting elements.

It is to be noted, however, that the aerogel layer is not essential;similar advantageous effects can be obtained even without the aerogellayer.

Embodiment 12

The light-emitting elements of Embodiments 1 to 11 can be applied, forexample, to display devices by arranging the light-emitting elements ina matrix so as to correspond to unit pixels. For example, after formingstripe-shaped reflective or transparent electrodes on a substrate,layers such as a light-emitting layer are deposited, and subsequentlystripe-shaped transparent electrodes are formed so as to be orthogonalto the above-described electrodes. By applying any voltage to the topand bottom electrodes of an element (pixel) which you want to emitlight, it is possible to make any light-emitting element (pixel) emitlight at a given luminance.

Furthermore, the light-emitting elements of Embodiments 1 to 11 can beapplied, for example, to lighting devices such as a backlight, byforming light-emitting elements over the entire surface of a substrate.

Embodiments 1 to 11 described the case where light was extracted fromthe opposite side from the substrate, but the present invention is notlimited to such a construction; it is also possible to make theconstruction one in which, for example, a very thin film substrate isused so that light is extracted from the substrate side.

EXAMPLE 1

As shown in FIG. 13, a light-emitting element of Example 1 has, on asubstrate 51, a reflective electrode 52, an electron-injecting layer 53,an electron transport luminescent material layer 54, a hole transportmaterial layer 55, a buffer layer 56, a transparent electrode 57, anaerogel layer 58, and a passivation layer 59, stacked on top of eachother in this order. The element was fabricated as follows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate 51, was prepared. On the substrate, Al was vapor-deposited bysputtering to form an Al film with a thickness of about 250 nm, and thenthe Al film was patterned in a given configuration by photolithographyto form the reflective electrode 52. Subsequently, by resistive heatingevaporation, an electron-injecting layer made of Li (with a thickness of1.5 nm), an electron transport luminescent material layer made of Alq₃(with a thickness of 50 nm), a hole transport material layer made of TPD(with a thickness of 50 nm), and a buffer layer made of copperphthalocyanine (with a thickness of 5 nm) were formed. Then, atransparent electrode made of ITO (with a thickness of 220 nm) wasformed by sputtering at room temperature (about 20° C.). Thereafter, anaerogel layer (with a thickness of 2 μm) was formed by coating andheating, and then a passivation layer (with a thickness of 20 μm) wasformed by sputtering. Thus, a light-emitting element shown in FIG. 13was fabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission (peak wavelength: 550 nm) wasobserved from the transparent electrode side. At this time, the elementobtained such a current efficiency (cd/A) as to be given in Table 1shown below, and such an extraction efficiency T as to be shown in FIG.25. The distance between the surface of a light-emitting region(electron transport luminescent material layer 54) facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 275 nm, which was 50% of the peakwavelength of light. In FIG. 25, λ represents the peak wavelength and drepresents the distance between the surface of the light-emitting regionfacing the aerogel layer side and the surface of the aerogel layerfacing the light-emitting region side.

EXAMPLE 2

A light-emitting element was fabricated in a manner similar to Example1, except that the electron-injecting layer, electron transportluminescent material layer, hole transport material layer, buffer layer,and transparent electrode were made to thicknesses of 1.5 nm, 50 nm, 50nm, 5 nm, and 110 nm, respectively.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 165 nm, which was 30% of the peakwavelength of light.

EXAMPLE 3

A light-emitting element was fabricated in a manner similar to Example1, except that the electron-injecting layer, electron transportluminescent material layer, hole transport material layer, buffer layer,and transparent electrode were made to thicknesses of 1.5 nm, 50 nm, 50nm, 5 nm, and 55 nm, respectively.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 110 nm, which was 20% of the peakwavelength of light.

EXAMPLE 4

A light-emitting element was fabricated in a manner similar to Example1, except that the electron-injecting layer, electron transportluminescent material layer, hole transport material layer, buffer layer,and transparent electrode were made to thicknesses of 1.5 nm, 50 nm, 20nm, 5 nm, and 30 nm, respectively.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 55 nm, which was 10% of the peakwavelength of light.

EXAMPLE 5

As shown in FIG. 14, a light-emitting element of Example 5 has, on asubstrate 51, a reflective electrode 52 with an irregular surface, anelectron-injecting layer 53, an electron transport luminescent materiallayer 54, a hole transport material layer 55, a buffer layer 56, atransparent electrode 57, and a passivation layer 59, stacked on top ofeach other in this order. The element was fabricated as follows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate 51, was prepared. On the substrate, Al was vapor-deposited bysputtering to form an Al film with a thickness of about 250 nm, and thenthe Al film was patterned in a given configuration by photolithography.Thereafter, the Al film was heat-treated at 400° C., thereby forming anirregular-shaped reflective electrode with a surface roughness (R_(max))of 150 nm (which was about 0.27 times the peak wavelength of light).Subsequently, by resistive heating evaporation, an electron-injectinglayer made of Li (with a thickness of 1.5 nm), an electron transportluminescent material layer made of Alq₃ (with a thickness of 50 nm), ahole transport material layer made of TPD (with a thickness of 50 nm),and a buffer layer made of copper phthalocyanine (with a thickness of 5nm) were formed. Then, by sputtering at room temperature, a transparentelectrode made of ITO (with a thickness of 250 nm) and a passivationlayer made of SiO₂ (with a thickness of 5500 nm) were formed. Thus, alight-emitting element shown in FIG. 14 was fabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 5805 nm, which was 1000% or more of thepeak wavelength of light.

EXAMPLE 6

As shown in FIG. 15, a light-emitting element of Example 6 has, on asubstrate 51, a reflective electrode 52 with an irregular surface, anelectron-injecting layer 53, an electron transport luminescent materiallayer 54, a hole transport material layer 55, a buffer layer 56, and atransparent electrode 57, stacked on top of each other in this order.The element was fabricated as follows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate 51, was prepared. On the substrate, Al was vapor-deposited bysputtering to form an Al film with a thickness of about 250 nm, and thenthe Al film was patterned in a given configuration by photolithography.Thereafter, the Al film was heat-treated at 400° C., thereby forming anirregular-shaped reflective electrode with a surface roughness (R_(max))of 150 nm (which was about 0.27 times the peak wavelength of light).Subsequently, by resistive heating evaporation, an electron-injectinglayer made of Li (with a thickness of 1.5 nm), an electron transportluminescent material layer made of Alq₃ (with a thickness of 50 nm), ahole transport material layer made of TPD (with a thickness of 50 nm),and a buffer layer made of copper phthalocyanine (with a thickness of 5nm) were formed. Then, a transparent electrode made of ITO (with athickness of 220 nm) was formed by sputtering at room temperature. Thus,a light-emitting element shown in FIG. 15 was fabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 275 nm, which was 50% of the peakwavelength of light. The same result regarding the distance was alsoobtained in Examples 7 to 11, as will be described below.

EXAMPLE 7

As shown in FIG. 16, a light-emitting element of Example 7 has, on asubstrate 51 with an irregular surface, a reflective electrode 52 formedso as to conform to the irregular shape, an electron-injecting layer 53,an electron transport luminescent material layer 54, a hole transportmaterial layer 55, a buffer layer 56, and a transparent electrode 57,stacked on top of each other in this order. The element was fabricatedas follows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate, was prepared, and a surface of the substrate was roughened bysandblasting. The surface roughness (R_(max)) of the roughened surfacewas 150 nm. On the substrate, Al was vapor-deposited by sputtering, andthen the Al film was patterned in a given configuration byphotolithography to form a reflective electrode (R_(max)=150 nm) with athickness of 250 nm so as to conform to the irregular shape of thesubstrate surface. Subsequently, by resistive heating evaporation, anelectron-injecting layer made of Li (with a thickness of 1.5 nm), anelectron transport luminescent material layer made of Alq₃ (with athickness of 50 nm), a hole transport material layer made of TPD (with athickness of 50 nm), and a buffer layer made of copper phthalocyanine(with a thickness of 5 nm) were formed. Then, a transparent electrodemade of ITO (with a thickness of 220 nm) was formed by sputtering atroom temperature. Thus, a light-emitting element shown in FIG. 16 wasfabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25.

EXAMPLE 8

As shown in FIG. 17, a light-emitting element of Example 8 has, on asubstrate 51, a reflective electrode 52 with an irregular surface, aplanarizing layer 61, an electron-injecting layer 53, an electrontransport luminescent material layer 54, a hole transport material layer55, a buffer layer 56, and a transparent electrode 57, stacked on top ofeach other in this order. The element was fabricated as follows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate 51, was prepared. On the substrate, Al was vapor-deposited bysputtering to form an Al film with a thickness of about 250 nm, and thenthe Al film was patterned in a given configuration by photolithography.Thereafter, the Al film was heat-treated at 400° C., thereby forming anirregular-shaped reflective electrode with a surface roughness (R_(max))of 150 nm (which was about 0.27 times the peak wavelength of light).Subsequently, a dispersion, in which polythiophene was dispersed inwater, was applied by spin coating and dried, thereby forming aplanarizing layer made of a conductive polymer (with a thickness of 10nm). Then, by resistive heating evaporation, an electron-injecting layermade of Li (with a thickness of 1.5 nm), an electron transportluminescent material layer made of Alq₃ (with a thickness of 50 nm), ahole transport material layer made of TPD (with a thickness of 50 nm),and a buffer layer made of copper phthalocyanine (with a thickness of 5nm) were formed. A transparent electrode made of ITO (with a thicknessof 220 nm) was formed by sputtering at room temperature. Thus, alight-emitting element shown in FIG. 17 was fabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25.

EXAMPLE 9

As shown in FIG. 18, a light-emitting element of Example 9 has, on asubstrate 51, a light-scattering layer 62 with an irregular surface, aplanarizing layer 61, a transparent electrode 63, a hole transportmaterial layer 55, an electron transport luminescent material layer 54,an electron-injecting layer 53, and a transparent electrode 57, stackedon top of each other in this order. The element was fabricated asfollows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate, was prepared. On the substrate, AgPdCu was vapor-deposited bysputtering to form an AgPdCu film with a thickness of about 250 nm.Subsequently, SiO₂ was vapor-deposited by sputtering at a substratetemperature of 400° C. during vapor-deposition, thereby forming alight-scattering layer with a surface roughness (R_(max)) of 150 nm(which was about 0.27 times the peak wavelength of light). After theformation of the SiO₂ film, the SiO₂ film was optically ground, therebyforming a planarizing layer (with a thickness of 200 nm). On theplanarizing layer, ITO was vapor-deposited by sputtering to form atransparent electrode (with a thickness of 100 nm). Thereafter, byresistive heating evaporation, a hole transport material layer made ofTPD (with a thickness of 50 nm), an electron transport luminescentmaterial layer made of Alq₃ (with a thickness of 50 nm), and anelectron-injecting layer made of MgAg (with a thickness of 1.5 nm) wereformed. The MgAg film also serves as a buffer layer. The MgAg film wasformed by co-depositing Mg and Ag, and made such that Mg:Ag=10:1 ratio(by weight) by controlling their co-deposition rates. Then, ITO wasvapor-deposited by sputtering to form a transparent electrode (with athickness of 220 nm). Thus, a light-emitting element shown in FIG. 18was fabricated.

When a positive voltage was applied to the bottom transparent electrodeof the thus-obtained light-emitting element and a negative voltage tothe top transparent electrode, green light emission was observed fromthe top transparent electrode side. At this time, the element obtainedsuch a current efficiency (cd/A) as to be given in Table 1 shown below,and such an extraction efficiency T as to be shown in FIG. 25.

EXAMPLE 10

For the planarizing layer in Example 9, polymethyl methacrylate (PMMA)was used in place of SiO₂. Specifically, there was prepared a solutionin which PMMA was dissolved in diethylene glycol ethyl methyl ether, andthe solution was applied, by spin coating, to a light-scattering layerwith an irregular surface and dried, thereby forming a planarizinglayer. It is to be noted that when a planarizing layer is thus formed,surface treatments such as optical grinding are not required.

When a positive voltage was applied to the bottom transparent electrodeof the thus-obtained light-emitting element and a negative voltage tothe top transparent electrode, green light emission was observed fromthe top transparent electrode side. At this time, the element obtainedsuch a current efficiency (cd/A) as to be given in Table 1 shown below,and such an extraction efficiency T as to be shown in FIG. 25.

EXAMPLE 11

As shown in FIG. 19, a light-emitting element of Example 11 has, on asubstrate 51, a reflective electrode 52, an electron-injecting layer 53,an electron transport luminescent material layer 54, a hole transportmaterial layer 55, a buffer layer 56, and a transparent electrode 57with an irregular surface, stacked on top of each other. The element wasfabricated as follows.

First, a glass substrate with a thickness of 0.7 mm, serving as thesubstrate, was prepared. On the substrate, Al was vapor-deposited bysputtering to form an Al film with a thickness of about 250 nm. The Alfilm was then patterned in a given configuration by photolithography toform a reflective electrode. Subsequently, by resistive heatingevaporation, an electron-injecting layer made of Li (with a thickness of1.5 nm), an electron transport luminescent material layer made of Alq₃(with a thickness of 50 nm), a hole transport material layer made of TPD(with a thickness of 50 nm), and a buffer layer made of copperphthalocyanine (with a thickness of 5 nm) were formed. Then, ITO wasvapor-deposited by sputtering at room temperature to form an ITO filmwith a thickness of 220 nm. The ITO film was irradiated with an argonion beam and etched, thereby forming a transparent electrode with anirregular surface (R_(max)=150 nm, which was about 0.27 times the peakwavelength of light). Thus, a light-emitting element shown in FIG. 19was fabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25.

EXAMPLE 12

A light-emitting element was fabricated in a manner similar to Example6, except that the electron-injecting layer, electron transportluminescent material layer, hole transport material layer, buffer layer,and transparent electrode were made to thicknesses of 1.5 nm, 50 nm, 50nm, 5 nm, and 110 nm, respectively.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 165 nm, which was 30% of the peakwavelength of light.

EXAMPLE 13

A light-emitting element was fabricated in a manner similar to Example6, except that the electron-injecting layer, electron transportluminescent material layer, hole transport material layer, buffer layer,and transparent electrode were made to thicknesses of 1.5 nm, 50 nm, 50nm, 5 nm, and 55 nm, respectively.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 110 nm, which was 20% of the peakwavelength of light.

EXAMPLE 14

A light-emitting element was fabricated in a manner similar to Example6, except that the electron-injecting layer, electron transportluminescent material layer, hole transport material layer, buffer layer,and transparent electrode were made to thicknesses of 1.5 nm, 50 nm, 20nm, 5 nm, and 30 nm, respectively.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25. The distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side was 55 nm, which was 10% of the peakwavelength of light.

EXAMPLES 15 TO 23

Light-emitting elements were fabricated in a manner similar to Examples6 to 14, except that the aerogel layer and passivation layer, similar tothose used in Example 1, were provided on a transparent electrode.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting elements and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the elements obtained suchcurrent efficiencies (cd/A) as to be given in Table 1 shown below, andsuch extraction efficiencies T as to be shown in FIG. 25. In theelements, the distance between the surface of the light-emitting regionfacing the aerogel layer side and the surface of the aerogel layerfacing the light-emitting region side was the same as that obtained ineach of Examples 6 to 14.

EXAMPLE 24

As shown in FIG. 20, a light-emitting element of Example 24 has, on asubstrate 51, reflective electrodes 52, a light-scattering layer 65 withan irregular surface, and an insulating layer 66, an electron-injectinglayer 53, an electron transport luminescent material layer 54, a holetransport material layer 55, a buffer layer 56, and a transparentelectrode 57, stacked on top of each other. The element was fabricatedin the manner shown in FIGS. 21 to 24.

First, as shown in FIG. 21, a glass substrate 51 with a thickness of 0.7mm was prepared. AgPdCu was vapor-deposited on the substrate bysputtering to form an AgPdCu film 65 a with a thickness of 300 nm. Then,the AgPdCu film 65 a was heat-treated at 400° C., thereby forming anAgPdCu film 65 b with an irregular surface (R_(max)=150 nm, which wasabout 0.27 times the peak wavelength of light). Subsequently, the AgPdCufilm 65 b with an irregular surface was patterned in a givenconfiguration by photolithography to form a light-scattering layer 65.

Next, as shown in FIG. 22, SiO₂ was vapor-deposited by sputtering so asto cover the light-scattering layer 65, thereby forming an SiO₂ film 66a with a thickness of 50 nm. The SiO₂ film was then patterned in a givenconfiguration by photolithography to form an insulating layer 66.

Then, as shown in FIG. 23, Al was vapor-deposited by sputtering to forman Al film 52 a with a thickness of 300 nm. Thereafter, the Al film waspatterned in a given configuration by photolithography to form areflective electrode 52 in the form of an island.

Subsequently, as shown in FIG. 24, by resistive heating evaporation, anelectron-injecting layer 53 made of Li with a thickness of 1.5 nm, anelectron transport luminescent material layer 54 made of Alq₃ with athickness of 50 nm, a hole transport material layer 55 made of TPD witha thickness of 50 nm, and a buffer layer 56 made of copperphthalocyanine with a thickness of 5 nm were sequentially formed. Then,ITO was vapor-deposited by sputtering at room temperature to form atransparent electrode 57 with a thickness of 110 nm. Thus, alight-emitting element shown in FIG. 20 was fabricated.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25.

The distance between the surface of the light-emitting region facing theaerogel layer side and the surface of the aerogel layer facing thelight-emitting region side was 165 nm, which was 30% of the peakwavelength of light.

COMPARATIVE EXAMPLE 1

On a transparent substrate, a transparent electrode made of ITO, abuffer layer made of copper phthalocyanine, a hole transport materiallayer made of TPD, an electron transport luminescent material layer madeof Alq₃, an electron-injecting layer made of Li, and a reflectiveelectrode made of Al were sequentially deposited. That is, the elementwas such that the layers according to the construction of Example 1 werestacked upside down on top of each other on the substrate. Thethicknesses of all the layers were made to be the same as those inExample 1.

When a positive voltage was applied to the transparent electrode of thethus-obtained light-emitting element and a negative voltage to thereflective electrode, green light emission was observed from thetransparent electrode side. At this time, the element obtained such acurrent efficiency (cd/A) as to be given in Table 1 shown below, andsuch an extraction efficiency T as to be shown in FIG. 25.

TABLE 1 Light-Scattering Current Efficiency Example d/λ Portion (cd/A) 1 0.5 Absent 5.0  2 0.3 Absent 7.5  3 0.2 Absent 8.2  4 0.1 Absent 10.0 5 >10 Present 6.8 6–11, 15–20 0.5 Present 7.8 12, 21 0.3 Present 8.313, 22 0.2 Present 10.0 14, 23 0.1 Present 11.5 24 0.3 Present 9.5Comparative >10 Absent 4.0 Example 1

From Table 1 and FIG. 25, it can be seen that the light-emittingelements of Examples 1 to 24 have higher current efficiencies and higherextraction efficiencies T than the light-emitting element of ComparativeExample. In particular, when the distance between the surface of thelight-emitting region facing the aerogel layer side and the surface ofthe aerogel layer facing the light-emitting region side is 30% or lessof the peak wavelength of light (preferably 20% or less, andparticularly preferably 10% or less), or when the scattering surface ispresent, the current efficiency and the extraction efficiency T aresignificantly increased.

When the distance between the surface of the light-emitting regionfacing the aerogel layer side and the surface of the aerogel layerfacing the light-emitting region side is 10% or less of the peakwavelength of light, the extraction efficiency T can be approximated bythe following Equation (2). In Equation (2), d represents the distancebetween the surface of the light-emitting region facing the aerogellayer side and the surface of the aerogel layer facing thelight-emitting region side, and λ represents the peak wavelength oflight.T=1−d/λ  (2)

Incidentally, using glass substrates and a plurality of light-emittingelements of Example 24, there were fabricated a substrate provided withlight-emitting elements that satisfied the foregoing Equation (1) and asubstrate provided with light-emitting elements that did not satisfy theforegoing Equation (1). Then, a voltage was applied to only onelight-emitting element of each of the substrates provided withlight-emitting elements to allow the one element to emit light, andleaked light from the light-extracting surfaces of light-emittingelements adjacent to the one element was examined. It was confirmed thata rather large amount of leaked light was detected with the substrateprovided with light-emitting elements that did not satisfy the foregoingEquation (1), as compared with the substrate provided withlight-emitting elements that satisfied the foregoing Equation (1).

1. A light-emitting element having a layered structure, the layeredstructure comprising at least a light-emitting layer having alight-emitting region, the light-emitting element comprising, a layerwith a refractive index of approximately 1, wherein a distance between asurface of the light-emitting region facing a side of the layer with arefractive index of approximately 1 and a surface of the layer with arefractive index of approximately 1 facing a side of the light-emittingregion, is limited to 50% or less of a peak wavelength of light.
 2. Thelight-emitting element according to claim 1, wherein on a substrate, alight reflective first electrode layer, the light-emitting layer, atransparent second electrode layer, and the layer with a refractiveindex of approximately 1 are provided in this order.
 3. Thelight-emitting element according to claim 2, wherein a passivation layeris formed on the layer with a refractive index of approximately
 1. 4.The light-emitting element according to claim 1, wherein on a substrate,a reflective layer, a first transparent electrode layer, thelight-emitting layer, a second transparent electrode layer, and thelayer with a refractive index of approximately 1 are provided in thisorder.
 5. The light-emitting element according to claim 4, wherein apassivation layer is formed on the layer with a refractive index ofapproximately
 1. 6. The light-emitting element according to claim 1,wherein the distance is limited to 30% or less of the peak wavelength oflight.
 7. The light-emitting element according to claim 2, wherein thedistance is limited to 30% or less of the peak wavelength of light. 8.The light-emitting element according to claim 3, wherein the distance islimited to 30% or less of the peak wavelength of light.
 9. Thelight-emitting element according to claim 4, wherein the distance islimited to 30% or less of the peak wavelength of light.
 10. Thelight-emitting element according to claim 5, wherein the distance islimited to 30% or less of the peak wavelength of light.
 11. Thelight-emitting element according to claim 1, wherein the distance islimited to 20% or less of the peak wavelength of light.
 12. Thelight-emitting element according to claim 2, wherein the distance islimited to 20% or less of the peak wavelength of light.
 13. Thelight-emitting element according to claim 3, wherein the distance islimited to 20% or less of the peak wavelength of light.
 14. Thelight-emitting element according to claim 4, wherein the distance islimited to 20% or less of the peak wavelength of light.
 15. Thelight-emitting element according to claim 5, wherein the distance islimited to 20% or less of the peak wavelength of light.
 16. Thelight-emitting element according to claim 1, wherein the distance islimited to 10% or less of the peak wavelength of light.
 17. Thelight-emitting element according to claim 2, wherein the distance islimited to 10% or less of the peak wavelength of light.
 18. Thelight-emitting element according to claim 3, wherein the distance islimited to 10% or less of the peak wavelength of light.
 19. Thelight-emitting element according to claim 4, wherein the distance islimited to 10% or less of the peak wavelength of light.
 20. Thelight-emitting element according to claim 5, wherein the distance islimited to 10% or less of the peak wavelength of light.
 21. Thelight-emitting element according to claim 1, wherein a distance tbetween a reflective layer and an interface is 500 μm or less.
 22. Thelight-emitting element according to claim 2, wherein a distance tbetween a reflective layer and an interface is 500 μm or less.
 23. Thelight-emitting element according to claim 3, wherein a distance tbetween a reflective layer and an interface is 500 μm or less.
 24. Thelight-emitting element according to claim 4, wherein a distance tbetween the reflective layer and an interface is 500 μm or less.
 25. Thelight-emitting element according to claim 5, wherein a distance tbetween the reflective layer and an interface is 500 μm or less.
 26. Thelight-emitting element according to claim 1, wherein the light-emittingelement comprises a light-scattering portion, and the light-emittingelement is for extracting light from a light-extracting surfacedistanced from the light-emitting region, the light being emitted fromthe light-emitting region.
 27. The light-emitting element according toclaim 26, wherein on a substrate, a light reflective first electrodelayer, the light-emitting layer, a transparent second electrode layer,and the layer with a refractive index of approximately 1 are provided inthis order.
 28. The light-emitting element according to claim 27,wherein a passivation layer is formed on the layer with a refractiveindex of approximately
 1. 29. The light-emitting element according toclaim 26, wherein on a substrate, a reflective layer, a firsttransparent electrode layer, the light-emitting layer, a secondtransparent electrode layer, and the layer with a refractive index ofapproximately 1 are provided in this order.
 30. The light-emittingelement according to claim 29, wherein a passivation layer is formed onthe layer with a refractive index of approximately
 1. 31. Thelight-emitting element according to claim 26, wherein the distance islimited to 30% or less of the peak wavelength of light.
 32. Thelight-emitting element according to claim 26, wherein the distance islimited to 20% or less of the peak wavelength of light.
 33. Thelight-emitting element according to claim 26, wherein the distance islimited to 10% or less of the peak wavelength of light.
 34. Thelight-emitting element according to claim 26, wherein a distance tbetween a reflective layer and an interface is 500 μm or less.
 35. Thelight-emitting element according to claim 26, wherein thelight-scattering portion corresponds to an irregular surface of areflective layer.
 36. The light-emitting element according to claim 26,wherein the light-scattering portion corresponds to an irregular surfaceof the light-extracting surface.
 37. The light-emitting elementaccording to claim 35, further comprising a planarizing layer forplanarizing the irregular surface.
 38. The light-emitting elementaccording to claim 36, further comprising a planarizing layer forplanarizing the irregular surface.
 39. The light-emitting elementaccording to claim 36, wherein a maximum value (R_(max)) of surfaceroughness of the irregular surface is ¼ or more of the peak wavelengthof light.
 40. The light-emitting element according to claim 26, whereinthe light-scattering portion is made of a base material and an additiveto be dispersed in the base material, the base material and the additivehaving different refractive indices.
 41. The light-emitting elementaccording to claim 1, further comprising a planarizing layer forplanarizing the irregular surface.
 42. The light-emitting elementaccording to claim 26, wherein an aerogel layer is used as the layerwith a refractive index of approximately
 1. 43. A display devicecomprising the light-emitting element in accordance with claim
 1. 44. Adisplay device comprising the light-emitting element in accordance withclaim
 26. 45. A lighting device comprising the light-emitting element inaccordance with claim
 1. 46. A lighting device comprising thelight-emitting element in accordance with claim 26.